On maturity, or lack thereof

A couple of years ago, a friend who was fast approaching his 25th birthday told me, "Life will never be the same on the wrong side of 25". I had no idea what he meant till I crossed 25 a few months ago. Gone are the glorious days when I could get away with murder with the excuse of being an adolescent. The days of good behaviour are here to stay. Time and again, I have to remind myself that I have no right to behave the way I do because I am more than a quarter of a century old. I need to display maturity,even if I really don't have that beast inside my head. I have to smile and say "How nice" when I feel like raising an eyebrow as if to say "What shit!". I must act nice with the stranger on the train who knows more about a lost love than I do whilst my heart is getting torn into shreds. I have to smile at someone I'd really like to slap. Worse still, I can't be myself with anyone anymore, not even my parents. Was I 21 just yesterday, stepping out into the world like a frisky little lamb? Why does it feel like this one year has aged me much more than the 24 before?